1. Field of the Invention
The present invention relates to a belted tire, and more specifically to a belted tire in which auxiliary layer arrangement over the outermost belt is improved for providing better tire uniformity.
2. Description of the Prior Art
With reference to Figs. 1A and 1B, the structure of a belted tire E will be described hereinbelow. The tire E is composed of a toroidal carcass 10, a main belt 20, and an auxiliary layer 30. The main belt 20 includes a first ply (layer) 20.sub.1 and a second ply 20.sub.2, for instance, each formed by arranging non-stretchable cords 21.sub.1 or 21.sub.2 so as to cross the tire equatorial plane C (central circumference) at a small angle over the carcass 10 and laid one upon another so that the arranged cords of the two plies intersect each other. The auxiliary layer 30 is formed by arranging heat-shrinkable cords 31 on the outermost layer of the main belt 20 substantially over all of the belt 20 in parallel to the equatorial plane C for providing a hoop effect. Further, in FIG. 1A, T denotes a tire tread formed on a crown portion of the tire E.
The auxiliary layer 30 is formed by winding a sheet made of heat-shrinkable cords under tension and by bonding both the ends 30A and 30B of the sheet 30 laid overlapping each other by a distance S.
A green tire thus formed is put into a vulcanizing metallic mold for vulcanization. In this process, there exists a problem in that the diameter of the green tire increases a little and therefore the bonding area M of the auxiliary layer 30 is dislocated in the tire circumferential direction by a distance corresponding to an increase in the tire diameter. This is because a bladder press (for simultaneously forming and vulcanizing a pneumatic tire) pressurizes and heats the green tire from the inside thereof by steam.
The above-mentioned drawbacks can be confirmed through an X-ray photograph. FIG. 1B shows a distortion of the main belt 20 near the bonding area M of the auxiliary layer 30, in which the first ply 20.sub.1 and the second ply 20.sub.2 both arranged symmetrical with respect to the equatorial plane at least in the auxiliary layer forming process are deformed and vulcanized, due to heat and pressure applied from the bladder press to the tire.
The belted tire in which the main belt 20 is not uniformly formed along the tire circumferential direction as described above involves various problems with respect to tire performance, in particular, from the viewpoint of LFV (lateral force variation), thus degrading traveling stability, durability, riding comfort, etc.